1. Field of the Invention
The present invention relates to a rotary head drum device for use in a video tape recorder (VTR) or the like.
2. Description of the Related Art
FIG. 5 is a schematic side view of a rotary head drum device in the related art.
Referring to FIG. 5, reference numeral 51 generally denotes the rotary head drum device. The rotary head drum device 51 is generally constructed of a drum base 52 and a head drum 53 provided on the drum base 52. The drum base 52 is adapted to be fixedly mounted on a chassis of a video tape recorder (not shown).
The head drum 53 is generally constructed of a rotating drum 54, a fixed drum 55 provided under the rotating drum 54, and a motor 56 provided under the fixed drum 55. A rotating shaft (not shown) is rotatably supported at a lower portion thereof by the fixed drum 55. The rotating drum 54 is fixed to the rotating shaft at an upper portion thereof, so that the former is rotatable together with the latter.
A tape lead 57 is formed as a stepped portion on the outer circumferential surface of the fixed drum 55 to define a passage along which a magnetic tape 64 travels. That is, the magnetic tape 64 is wound around the outer circumferential surfaces of the rotating drum 54 and the fixed drum 55 as being guided by the tape lead 57. In this condition, the magnetic tape 64 is driven by a driving means (not shown) to run along the tape lead 57.
A plurality of magnetic heads 58 are fixedly mounted on the lower surface of the rotating drum 54 opposed to the upper surface of the fixed drum 55. A plurality of windows 59 are formed on the outer circumferential surface of the rotating drum 54 so as to correspond to the magnetic heads 58. The tips of the magnetic heads 58 slightly project from the respective windows 59 to the outside of the rotating drum 54 in the radial direction thereof. A rotor (not shown) of the motor 56 is fixedly mounted through the rotating shaft to the rotating drum 54, and a stator (not shown) of the motor 56 is fixedly mounted to the lower surface of the fixed drum 55 at a radially outside portion thereof by means of screws 65.
The head drum 53 is fixed through a plurality of metal mounting sheets 60 to the drum base 52 by using screws 61 and 63. A plurality of mounting portions 62 for mounting the metal mounting sheets 60 are formed on the upper surface of the drum base 52 at three positions substantially equally spaced from a center of the rotating shaft and substantially equally spaced from each other in the circumferential direction. Each metal mounting sheet 60 is fixed at one end thereof to the lower surface of the motor 56 by means of each screw 61. Each mounting portion 62 is formed with a tapped hole (not shown) for threadedly engaging each screw 63. The metal mounting sheets 60 fixed to the motor 56 are mounted on the respective mounting portions 62, and the screws 63 are tightened thereto to fix the metal mounting sheets 60. Accordingly, if the dimensional accuracy of each mounting portion 62 is not good or the degree of tightening of each screw 63 is not uniform, the dimensional accuracy of the tape lead 57 required for high working accuracy, such as several .mu.m, cannot be satisfied.
In a recording or reproducing operation of the rotary head drum device 51, the rotating drum 54 is rotated at a high speed in a direction depicted by an arrow A in FIG. 5, and the magnetic tape 64 travels in a direction depicted by an arrow B in FIG. 5. Further, when the rotating drum 54 is rotated, the tips of the magnetic heads 58 mounted on the rotating drum 54 are sequentially brought into sliding contact with the magnetic tape 64 traveling in the wound condition around the outer circumferential surfaces of the rotating drum 54 and the fixed drum 55, thereby effecting recording or reproduction.
In the rotary head drum device 51, the metal mounting sheets 60 fixed to the motor 56 are first mounted on the respective mounting portions 62 of the drum base 52, and the screws 63 are then tightened to the mounting portions 62 to fix the metal mounting sheets 60. Thus, the head drum 53 is fixed through the metal mounting sheets 60 to the drum base 52. The use of the metal mounting sheets 60 is due to the following reasons: if the metal mounting sheets 60 are not used, the fixed drum 55 would be fixed at its outer circumferential portion to the drum base 52 by means of screws. However, in this case, the fixing of the fixed drum 55 is hindered by the motor 56 because the motor 56 is provided under the fixed drum 55. Further, if the screws for fixing the fixed drum 55 to the drum base 52 are strongly tightened, a strain due to a low rigidity of the fixed drum 55 would be generated to have an adverse effect on the accuracy of the tape lead 57 requiring a high accuracy such as several .mu.m. Accordingly, much time would be required to remove the above adverse effect by adjusting a degree of tightening of each screw. However, since the above structure employs the many screws 61, 63 and 65, a material cost and an assembling cost are increased.